Improved roadway surfaces for the support and passage of vehicles, for example, streets, highways and air fields, have long been constructed from cementitious materials such as concrete and asphalt. As is well known, the construction of roadways from such cementitious materials consumes a great deal of time, due both to the preparation of the subgrade and the curing of the cast or poured pavement. For example, while cement offers substantial advantage in such structures due to its strength, permanency and relatively low cost, it must be cured or hardened slowly over a period of about a week, during which time it must be protected from vibration, freezing and a too-rapid rate of drying. Asphalt and other coal-tar derivatives, while attaining a fair degree of strength upon cooling, require heating of various hydrocarbon derivatives and specialized application techniques in order to provide any degree of compressive strength. Accordingly, it has been a desideratum to provide a material which may be employed to rapidly and easily allow the repair of cementitious roadways.
This desire has been felt not only with regard to the repair of pot holes and the like in highways, but is particularly important in the repair of damaged runways, e.g., the repair of bomb-damaged air fields.
The optimal rapid repair system for any roadway must be structurally sound, cure virtually flush with the surrounding pavement, and be rapidly accomplished under a wide variety of temperatures and weather conditions.
Rapid runway repair has been accomplished by several methods, which proceed by first filling a roadway depression with an aggregate, such as pavement debris or crushed stone, followed by placing a rigid covering over the fill. The cover has comprised preformed metallic or concrete slabs which are anchored to existing pavement which surrounds the damaged portion. However, since these coverings must be of appreciable thickness to withstand the loads imposed by passing traffic, the transport and placement of such slabs is a significant impediment to rapid repair. Moreover, the aggregate must be carefully levelled to enable the placement of the covering flush with the existing pavement. In addition, the anchoring of such material to the surrounding pavement often creates a raised portion which may cause damage to vehicles which traverse the repair at any appreciable speed.
Poured-in-place structural caps have also been employed over the above-described aggregate fill material. This type of repair employs rapid-setting materials which have substantial flexural strength which are poured into the depression, and cure to form a flush cap above the fill material. In order to provide sufficient strength over low-strength subgrades, this cap may be as much as twelve inches thick.
Due to the problems set forth above, a number of polymer concrete materials have been proposed, along with methods for their use. For example, an acrylic polymer, methylmethacrylate, has been tested and found to provide a structural cap crater repair material which may be poured flush with the surrounding pavement. One disadvantage of the methylmethacrylate polymer concrete has been the high flammability of the monomeric precursors, which may cause substantial problems both in the storage and use of the material.
Water incompatability has been a major problem with nearly all polymers, as water is invariably found in aggregate material or in the subgrade beneath the pavement. In addition, a water intolerant material would not be usable during any amount of rainfall. Accordingly, others have selected furfuryl alcohol polymers and unsaturated polyesters to develop water-compatible systems. In addition, various water-absorbing additives have been treated, such as Portland cement and silica flour. Magnesium polyphosphate cement formulations have also been employed which permit moisture contents of up to 3 weight percent.
Polyurethane formulations have heretofore been incapable of providing satisfactory roadway repair material, particularly under wet placement conditions as the ambient moisture in the aggregate or standing water in the crater react undesirably with the isocyanate component in such formulations. This isocyanate-water reaction not only yields a low-strength polymer concrete, but also contributes to a somewhat spongy consistency of the cured material due to the formation of carbon dioxide bubbles during the polymerization reaction. Moreover, any standing water in the crater will cause the urethane to foam, and the polymer thus swells and raises above the roadway surface.
The above-described problems are most apparent when the rapid repair of bomb-damaged air fields during hostilities is attempted. The repair of air field pavements damaged by various weapons must be completed rapidly following an attack in order to launch retaliatory missions. Any repair method or material which is disposed above the level of the surrounding pavement, creating a raised portion on the runway, presents special problems for militry aircraft due, in part, to high runway speeds and heavy cargos.
For example, the repair diameter of a crater formed from the explosion of a 750 lb. bomb can measure as much as sixty feet, with a depth approaching fifteen feet. As a further complication, any repair material must be placed in less than thirty minutes under adverse battle conditions and under environmental extremes, i.e., temperatures ranging from -25.degree. F. to 125.degree. F. and at rainfall rates of in excess of one inch per hour.
Further, the flammability of cured polymer concrete has presented a particular problem in military operations. For example, in one recent test, a freshly cured polyurethane repair such as described above was set afire by hevy construction equipment involved in the repair.
According to the present invention, methods and materials are provided for the formulation of a solution which may be caused to quickly percolate through at least a portion of an aggregate fill in a crater or other depression to rapidly form a polyurethane concrete which is flush with the surrounding grade. The solution is hydrophobic and has a specific gravity greater than that of water so that any ambient moisture within the crater is displaced. The combination of catalysts in the solution provide a cure rate which virtually eliminates any water-isocyanate reaction in the polymer precursor during the displacement of water, and the combination may be varied to allow cure times of as little as one second and to allow constant cure rates at temperatures of from -20.degree. F. to 125.degree. F. As described in the preferred embodiment, the present invention provides an all-weather flush and nonflammable pavement repair which is capable of supporting vehicular traffic in as little as thirty minutes.